The optical efficiency of deep-ultraviolet nitride-based heterostructures emitting at wavelengths around 215 nm remains severely limited by thermally activated non-radiative recombination processes. In this article, we investigate the optical properties of high-quality Ga0.2Al0.8N multiple quantum wells grown by molecular beam epitaxy on AlN templates fabricated either by metal-organic chemical vapor deposition or by molecular beam epitaxy. The temperature-dependent photoluminescence measurements performed in the 10-300 K range reveal that the thermal quenching of the photoluminescence emission is governed by three distinct activation processes common to all the sample series. The first non-radiative recombination channel, characterized by an activation energy in the 4 8 meV range, is extrinsic in origin and is associated with impurities as well as with the density of structural defects within the crystal. The second process, with an activation energy of 70 meV is intrinsic in nature and is related to the thermal dissociation of the free exciton. A third thermally activated process, also intrinsic, exhibits an activation energy of approximately 130 meV and is assigned to the thermal escape of the spin-orbit split off holes from the active region of the multiple quantum wells, leading to a further reduction in optical efficiency at elevated temperatures.